Various instruments have been developed to test electrical components in vehicles for operability. Such instruments include voltmeters, ammeters and continuity testers. Some of these instruments have been incorporated into hand-held units such that these tests can be easily performed. One such hand-held instrument is a digital multimeter marketed by the assignee of the present invention under Model 2880. This instrument tests solid state electronics, computer and electronic ignition dwell, electronic and conventional ignition systems, and diodes.
Hand-held instruments have also been developed which have the capability to test certain engine sensors and ignition modules in vehicles. However, it is believed that these instruments are generally limited in their flexibility in testing a wide variety of sensors and/or ignition modules, and in testing these components in different types of vehicles. For example, it is known that hand-held instruments have been developed that test potentiometer-type sensors (e.g., throttle position and EGR position), temperature sensors (e.g., engine coolant, incoming air), Hall effect sensors and/or ignition modules in vehicles; while other hand-held instruments have been developed which have the capability to test oxygen, knock and/or reluctance sensors. In general, potentiometer-type, temperature and Hall effect sensors, and ignition modules, are checked for operability by applying a voltage across the sensor or module, exercising the sensor or module, and observing whether the resistance has changed across the sensor or module. On the other hand, oxygen, knock and reluctance sensors are generally tested by exercising the sensor, and comparing the output voltage of the sensor with a reference voltage. It is believed that these different types of test instruments have been developed heretofore because of the different testing requirements for the engine components.
By way of example, one type of test instrument developed exclusively for Hall effect sensors is shown in Bates, Jr., U.S. Pat. No. 5,032,791. This test instrument apparently provides a visual indication of the operativeness of the Hall effect device when it is coupled to the device. However, the Bates test instrument is limited in its applicability to other types of engine sensors or ignition modules, or even to test the continuity of a circuit. In other words, the Bates test instrument is designed for a specific application and has limited flexibility. To test other vehicle components, for example potentiometer-type and temperature sensors, ignition modules, and oxygen, knock and reluctance sensors, additional instruments or adapters are necessary. However, expense is incurred in having to purchase a multitude of different test instruments or adapters for a vehicle engine. Further, having various test instruments for a vehicle engine can complicate the entire testing process.
Another type of hand-held test instrument is shown in Bates, Jr., U.S. Pat. No. 5,170,125. This test instrument is specifically designed to test the ignition module of a vehicle and to apparently provide a visual indication of the operativeness of this device. However, this instrument also has limited flexibility in being able to test other vehicle components, such as the various engine sensors, and hence suffers from the same drawbacks identified above.
Further, in addition to an instrument's ability to test a variety of engine components, it is important that a test instrument have the capability to test these components on a number of different types of vehicles (e.g., makes, models, etc), for these engine components can be manufactured slightly differently by the various vehicle manufacturers, and hence can have different responses during the testing process. Finally, it is important that such an instrument have protection from circuit overload, incorrect connection, shorts, etc., such that the instrument is not damaged during the tests.
Accordingly, there is a demand in the industry for a single, integral, hand-held instrument which tests a broad range of vehicle components such as various engine sensors and ignition modules, and tests such components on a broad range of vehicles. Further, there is a demand in the industry for a simple and convenient instrument of the above-mentioned type which includes protection from overload, incorrect connection to the vehicle, and shorting, such that the instrument is not damaged through improper use.